1. Field of the Invention
The invention relates to a fault determination device and a fault determination method of a negative pressure generation device. More particularly, the invention relates to a fault determination device of a negative pressure generation device which determines the presence/absence of an abnormality of the negative pressure generation device that has an ejector and which determines a cause of the abnormality.
2. Description of the Related Art
In vehicles, an ejector has been used to supply a brake booster with a negative pressure that is greater than the negative pressure that is to be extracted from an intake passageway of an intake system of an internal combustion engine (hereinafter, also referred to simply as “the intake system of the internal combustion engine”) that connects in communication from the atmosphere to the cylinders of the engine. Generally, the ejector is disposed in a bypass that bypasses the throttle valve, and generates great negative pressure due to the Venturi effect. With regard to the ejector, Japanese Patent Application Publication No. 2005-188332 discloses, for example, an ejector device shown below. This ejector device has switch means for switching between the operation and the non-operation of the ejector, and clog determination means for determining whether or not a channel of the ejector is clogged on the basis of a difference between the amounts of air that are taken into an intake pipe before and after the operation switching performed by the switch means. That is, the ejector device proposed by the Japanese Patent Application Publication No. 2005-188332 is a technology of determining the occurrence of a clogging of a channel of the ejector on the basis of a fact that operation of the ejector cause the intake air flow amount to vary, that is, on condition that no change occur in the intake air flow amounts before and after the operation switching, the technology determines that the ejector has a channel clogging.
However, according to the foregoing related art, there is a possibility of failing to correctly determine that the ejector has a channel clogging in a situation shown below. The manner of connection of a bypass to the intake passageway may be, for example, connection upstream of the bypass to the intake passageway upstream of intake air flow amount detection means (e.g., an air flow meter). In this case, the bypass extends around not only the throttle valve but also the intake air flow amount detection means. Therefore, in this case, the intake air flowing through the bypass is not detected by the intake air flow amount detection means, and therefore, the related art always falsely determines that the ejector has a channel clogging. That is, in such a case, the aforementioned related art cannot be applied to the determination regarding the channel clogging. Furthermore, for example, even in the case where the bypass does not extend around the intake air flow amount detection means, there is also a possibility of failing to correctly detect a change in the intake air flow amount if the detection performance deteriorates because of adhering a foreign substance or if a fault occurs, or the like. Still further, the amount of change in the intake air flow amount is small in comparison with the total intake air flow amount, and it is not easy to distinguish a change in the intake air flow amount from an external disturbance or the like. As a result, a false determination of an external disturbance or the like as the change in the intake air flow amount ascribable to a channel clogging is conceivable.
Furthermore, if a deposit adheres to the throttle valve as a time-dependent change, the intake air flow amount at a fixed degree of throttle opening changes. At the same time, it is considered that in this case, the amount of change in the intake air flow amount in accordance with the operation and the non-operation of the ejector is also considered to change, and therefore a possibility of decline in the accuracy of determination is also considered to exist. Furthermore, for example, in the case where an increasing/decreasing correction of the intake air flow amount is performed so as to restrain variation of the idle rotation speed by an ISC (Idle Speed Control) in accordance with change in the state of operation of state change means, a normal state is a state where the rotation speed and the intake air flow amount of the internal combustion engine undergo substantially no change before and after the operation switching of the ejector. In this case, the aforementioned related art determines that the ejector has a channel clogging while the ejector is actually normal, and therefore the related art cannot be applied.
The cause of abnormality that occurs in the negative pressure generation device is not limited to the channel clogging. For example, it is conceivable as a cause that suction of atmospheric air is occurring in the negative pressure generation device because an air hose forming the bypass is disconnected or a crack or a hole is formed in the air hose. As other causes of abnormality, it is also conceivable that the state change means has an operation failure, so that the channel is fixed in a closed state and the ejector cannot be caused to function, or so that the channel is fixed in an open state and the ejector cannot be caused to stop functioning, or the like. Since a plurality of causes of abnormality are conceivable as indicated above, it is advantageous that if an abnormality occurs in the negative pressure generation device, it is possible to not only determine the presence/absence of an abnormality but also determine a cause of the abnormality. This makes it possible to easily detect a site of abnormality and promptly cope with the abnormality and therefore take an appropriate countermeasure, such as performing a tentative coping control in accordance with the cause of abnormality, etc.